Senses provide information about the body and its environment. Humans have five special senses: olfaction (smell), gustation (taste), equilibrium (balance and body position), vision, and hearing. Additionally, we possess general senses, also called somatosensation, which respond to stimuli like temperature, pain, pressure, and vibration.

Review Questions

Where does perception occur?

spinal cord

cerebral cortex

receptors

thalamus

B

If a person’s cold receptors no longer convert cold stimuli into sensory signals, that person has a problem with the process of ________.

reception

transmission

perception

transduction

D

After somatosensory transduction, the sensory signal travels through the brain as a(n) _____ signal.

electrical

pressure

optical

thermal

A

Free Response

If a person sustains damage to axons leading from sensory receptors to the central nervous system, which step or steps of sensory perception will be affected?

Transmission of sensory information from the receptor to the central nervous system will be impaired, and thus, perception of stimuli, which occurs in the brain, will be halted.

In what way does the overall magnitude of a stimulus affect the just-noticeable difference in the perception of that stimulus?

The just-noticeable difference is a fraction of the overall magnitude of the stimulus and seems to be a relatively fixed proportion (such as 10 percent) whether the stimulus is large (such as a very heavy object) or small (such as a very light object).

Somatosensation is a mixed sensory category and includes all sensation received from the skin and mucous membranes, as well from as the limbs and joints. Somatosensation is also known as tactile sense, or more familiarly, as the sense of touch. Somatosensation occurs all over the exterior of the body and at some interior locations as well. A variety of receptor types—embedded in the skin, mucous membranes, muscles, joints, internal organs, and cardiovascular system—play a role.

Review Questions

_____ are found only in _____ skin, and detect skin deflection.

Meissner’s corpuscles: hairy

Merkel’s disks: glabrous

hair receptors: hairy

Krause end bulbs: hairy

B

If you were to burn your epidermis, what receptor type would you most likely burn?

free nerve endings

Ruffini endings

Pacinian corpuscle

hair receptors

A

Free Response

What can be inferred about the relative sizes of the areas of cortex that process signals from skin not densely innervated with sensory receptors and skin that is densely innervated with sensory receptors?

The cortical areas serving skin that is densely innervated likely are larger than those serving skin that is less densely innervated.

Taste, also called gustation, and smell, also called olfaction, are the most interconnected senses in that both involve molecules of the stimulus entering the body and bonding to receptors. Smell lets an animal sense the presence of food or other animals—whether potential mates, predators, or prey—or other chemicals in the environment that can impact their survival. Similarly, the sense of taste allows animals to discriminate between types of foods.

Review Questions

Which of the following has the fewest taste receptors?

fungiform papillae

circumvallate papillae

foliate papillae

filiform papillae

D

How many different taste molecules do taste cells each detect?

one

five

ten

It depends on the spot on the tongue

A

Salty foods activate the taste cells by _____.

exciting the taste cell directly

causing hydrogen ions to enter the cell

causing sodium channels to close

binding directly to the receptors

A

All sensory signals except _____ travel to the _____ in the brain before the cerebral cortex.

vision; thalamus

olfaction; thalamus

vision; cranial nerves

olfaction; cranial nerves

B

Free Response

From the perspective of the recipient of the signal, in what ways do pheromones differ from other odorants?

Pheromones may not be consciously perceived, and pheromones can have direct physiological and behavioral effects on their recipients.

What might be the effect on an animal of not being able to perceive taste?

The animal might not be able to recognize the differences in food sources and thus might not be able to discriminate between spoiled food and safe food or between foods that contain necessary nutrients, such as proteins, and foods that do not.

Audition, or hearing, is important to humans and to other animals for many different interactions. It enables an organism to detect and receive information about danger, such as an approaching predator, and to participate in communal exchanges like those concerning territories or mating. On the other hand, although it is physically linked to the auditory system, the vestibular system is not involved in hearing. Instead, an animal’s vestibular system detects its own movement.

Art Connections

[link] Cochlear implants can restore hearing in people who have a nonfunctional cochlear. The implant consists of a microphone that picks up sound. A speech processor selects sounds in the range of human speech, and a transmitter converts these sounds to electrical impulses, which are then sent to the auditory nerve. Which of the following types of hearing loss would not be restored by a cochlear implant?

Hearing loss resulting from absence or loss of hair cells in the organ of Corti.

Hearing loss resulting from an abnormal auditory nerve.

Hearing loss resulting from fracture of the cochlea.

Hearing loss resulting from damage to bones of the middle ear.

[link] B

Review Questions

In sound, pitch is measured in _____, and volume is measured in _____.

nanometers (nm); decibels (dB)

decibels (dB); nanometers (nm)

decibels (dB); hertz (Hz)

hertz (Hz); decibels (dB)

D

Auditory hair cells are indirectly anchored to the _____.

basilar membrane

oval window

tectorial membrane

ossicles

A

Which of the following are found both in the auditory system and the vestibular system?

basilar membrane

hair cells

semicircular canals

ossicles

B

Free Response

How would a rise in altitude likely affect the speed of a sound transmitted through air? Why?

The sound would slow down, because it is transmitted through the particles (gas) and there are fewer particles (lower density) at higher altitudes.

How might being in a place with less gravity than Earth has (such as Earth’s moon) affect vestibular sensation, and why?

Because vestibular sensation relies on gravity’s effects on tiny crystals in the inner ear, a situation of reduced gravity would likely impair vestibular sensation.

Vision is the ability to detect light patterns from the outside environment and interpret them into images. Animals are bombarded with sensory information, and the sheer volume of visual information can be problematic. Fortunately, the visual systems of species have evolved to attend to the most-important stimuli. The importance of vision to humans is further substantiated by the fact that about one-third of the human cerebral cortex is dedicated to analyzing and perceiving visual information.

Review Questions

Why do people over 55 often need reading glasses?

Their cornea no longer focuses correctly.

Their lens no longer focuses correctly.

Their eyeball has elongated with age, causing images to focus in front of their retina.

Their retina has thinned with age, making vision more difficult.

B

Why is it easier to see images at night using peripheral, rather than the central, vision?

Cones are denser in the periphery of the retina.

Bipolar cells are denser in the periphery of the retina.

Rods are denser in the periphery of the retina.

The optic nerve exits at the periphery of the retina.

C

A person catching a ball must coordinate her head and eyes. What part of the brain is helping to do this?

hypothalamus

pineal gland

thalamus

superior colliculus

D

Free Response

How could the pineal gland, the brain structure that plays a role in annual cycles, use visual information from the suprachiasmatic nucleus of the hypothalamus?

The pineal gland could use length-of-day information to determine the time of year, for example. Day length is shorter in the winter than it is in the summer. For many animals and plants, photoperiod cues them to reproduce at a certain time of year.

How is the relationship between photoreceptors and bipolar cells different from other sensory receptors and adjacent cells?

The photoreceptors tonically inhibit the bipolar cells, and stimulation of the receptors turns this inhibition off, activating the bipolar cells.

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